In recent years, there have been actively made research and development of not only industrial robots but also consumer robots, which play various roles for people's livelihood. Among such robots, human-like robots (humanoid robot) being able to walk in erect posture are expected to be able to substitute for actions of human beings. In such humanoid robots, many joint parts are provided for imitating actions or motions of a human being, and a variety of motions having a plurality of degrees of freedom in the joint parts are required. For that reason, in each of the joint parts of the humanoid robots, the number of actuators such as servo-motors mounted therein increases corresponding to the degrees of freedom given to each joint part, with the result that it becomes difficult to reduce the size of each joint part due to this, and the structure and arrangement of the actuators are made complicated.
Here, for example, in patent literature 1, there is disclosed a joint part arrangement in which two actuators are arranged side by side (or in parallel) in a joint part of a robot, and an output shaft of each actuator is connected with a linkage mechanism which is formed of an intermediate link and an arm, wherein the arm of each linkage mechanism is connected with a base member of the joint part through a cross shaped universal coupling. In such a construction, when each actuator is made to carry out a predetermined action, a motion of two degrees of freedom can be achieved in the joint part, and in this technology, a motion of each degree of freedom is carried out by always driving the two actuators, as a result of which each actuator can be reduced in size, and the arrangement of the actuators is also such that both of the actuators are merely arranged in parallel.